Cavities can decay to tooth to the point where restoration is virtually impossible without a procedure called crown lengthening. Crown lengthening is a routine surgical procedure, which remodels the contour of the gum line. The procedure does not actually lengthen the crown (the part of the tooth we see in the mouth), but rather lowers the gum line. When there is not enough tooth structure to support a restoration or when the cavity is so deep that it is difficult to reach for removal, this is the only option. Sometimes a tooth has been broken below the gum line. In this instance, crown lengthening is very successful in exposing more of the tooth, so that the dentist has something to work with.